Biology Reference
In-Depth Information
turn brown; stalks fall over; roots are soft and
slimy inside the epidermis. Corms may rot so
fast the plant falls over without other symptoms,
or the diseased portion may dry down to sunken
dark spots, in which the bacteria stay dormant to
the next season.
On tomatoes, infection takes place through
growth cracks, insect wounds, or sunscald areas.
The tissue is at first water-soaked, then opaque,
and in 3 to 10 days the whole fruit is soft, watery,
colorless, with an offensive odor.
Control
Scrub calla corms, cut out rotted spots,
and let cork over for a day or two. Plant in fresh or
sterilized soil in sterilized containers and keep
pots on clean gravel or wood racks, never on
beds where diseased callas have grown previ-
ously. Grow at cool
apparently carried in seed; hot-water treatment
is helpful. Drenching delphinium crowns with
bordeaux mixture has been recommended in the
past. Insect larval control is helpful with potato.
Avoid excessive watering or irrigation.
Erwinia carotovora subsp. carotovora (for-
merly
Erwinia carotovora
var.
carotovora
).
Wilt
of sunflower, Kalancho¨; zucchini squash, and
draceana.
Soft Rot
, general on many vegetables,
in field, storage, and transit, and many ornamen-
tals, especially iris. The bacteria were first iso-
lated from rotten carrots, whence the name, but
they are equally at home in asparagus, cabbage,
turnips and other crucifers, celery, cucumber,
eggplant, endive, garlic, horseradish, melon,
parsnip, pepper, spinach, sunflower (stalk rot),
sweet potato, and tomato. Besides wide distribu-
tion on iris, soft rot has been reported, among
ornamentals, on chrysanthemum, dahlia, Easter
lily, geranium, orchid, sansevieria, poinsettia,
and yellow calla.
The bacteria enter through wounds, causing
a rapid, wet rot with a most offensive odor. The
middle lamella is dissolved, and roots become
soft and pulpy. Soft rot in iris often follows
borer infestation. Tips of leaves are withered,
the basal portions wet and practically shredded.
The entire interior of a rhizome may disintegrate
into a vile yellow mess while the epidermis
remains firm. The rot is more serious in shaded
locations, when iris is too crowded or planted too
deeply.
Control
Borer control, starting when fans are
6 inches high, has greatly reduced the incidence
of rot. If it appears, dig up the clumps, cut away
all rotted portions, cut leaves back to short fans.
Allow to dry in the sun for a day or two, then
replant in well-drained soil, in full sun with upper
portion of the rhizome slightly exposed. Many
good iris growers do not agree with this “sitting
duck” method, preferring to cover with an inch of
soil; but the sun is an excellent bactericide, and
shallow planting is one method of disease con-
trol. Clean off all old leaves in late fall after frost.
Prevent rot on stored vegetables by saving
only sound, dry tubers, in straw or sand, in
a well-ventilated room with temperature not too
much above freezing.
temperatures and avoid
overwatering.
Erwinia carotovora subsp. atroseptica (for-
merly
Erwinia carotovora
).
Potato Blackleg
,
Basal Stem Rot
,
Tuber Rot
, general on potato.
This is a systemic disease perpetuated by natu-
rally infected tubers. Lower leaves turn yellow;
upper leaves curl upward; stems and leaves tend
to grow up rather than spread out; stem is black-
spotted, more or less softened at base and up to
3 or 4 inches from ground, and may be covered
with bacterial slime; shoots may wilt and fall
over. Tubers are infected through the stem end.
The disease is most rapid in warm, moist weather,
and may continue in storage. The bacteria are
spread on the cutting knife, as with ring rot, and
by seed-corn maggots, and may persist for a time
in soil.
Control
Use certified seed potatoes and plant
whole tubers; if cut seed must be used, allow to
cork over to prevent infection from soil. Practice
long rotation; disinfest cutting knife. Late varie-
ties seem to be more resistant.
Erwinia carotovora subsp. atroseptica (for-
merly
Erwinia carotovora
).
Delphinium Black-
leg
,
Foot Rot
,
Bacterial Crown Rot
of perennial
Delphinium;
Stem and Bud Rot
of Rocket Lark-
spur. In delphinium there is a soft black discolor-
ation at the base of the stem, with bacteria oozing
out from cracks. In larkspur there is a black rot of
buds as well as yellowing of leaves, blackening of
stem,
stunting of plants. The bacteria are
In the garden,
rotate
